The syntax is the URL, plus the name of the file, eg:
<CODEBASE="http://www.houstonmedia.com/timewarp.ocx>
(don't bother looking for this particular control, 'cos I just made it up).
A typical ActiveX object on a page will look something like this:
<OBJECT ID="PowerPanels1" CLASSID="CLSID:7CDE26C3-A9A7-11CF-B509-
00A024488F73" WIDTH="256" HEIGHT="256" CODEBASE=../ocx/npwrpnl.cab>
<PARAM NAME="_Version" VALUE="65536">
<PARAM NAME="_ExtentX" VALUE="7867">
<PARAM NAME="_ExtentY" VALUE="7585">
<PARAM NAME="_StockProps" VALUE="0">
<PARAM NAME="panelcount" VALUE="4">
<PARAM NAME="panel0_image" VALUE="screen1.png">
<PARAM NAME="panel0_hlink" VALUE="http://www.ncompasslabs.com">
<PARAM NAME="panel0_duration" VALUE="2000">
<PARAM NAME="panel0_transitiontype" VALUE="SWIPELEFT">
<PARAM NAME="panel0_tilespeed" VALUE="10">
<PARAM NAME="panel1_image" VALUE="screen2.png">
<PARAM NAME="panel1_hlink" VALUE="http://www.ncompasslabs.com">
<PARAM NAME="panel1_duration" VALUE="2000">
<PARAM NAME="panel1_transitiontype" VALUE="SWIPERIGHT">
<PARAM NAME="panel1_tilespeed" VALUE="10">
<PARAM NAME="panel2_image" VALUE="screen3.png">
<PARAM NAME="panel2_hlink" VALUE="http://www.ncompasslabs.com">
<PARAM NAME="panel2_duration" VALUE="2000">
<PARAM NAME="panel2_transitiontype" VALUE="FLIPTOUR">
<PARAM NAME="panel2_tilespeed" VALUE="10">
<PARAM NAME="panel3_image" VALUE="screen4.png">
<PARAM NAME="panel3_hlink" VALUE="http://www.ncompasslabs.com">
<PARAM NAME="panel3_duration" VALUE="2000">
<PARAM NAME="panel3_transitiontype" VALUE="FLIPTOUL">
<PARAM NAME="panel3_tilespeed" VALUE="10">